SDL: Document the missing data argument to w/1, w/2, w/4
SDL: Document the missing data argument to w/1, w/2, w/4

Iniquitatis/mgba,zerofalcon/mgba,MerryMage/mgba,AdmiralCurtiss/mgba,zerofalcon/mgba,Touched/mgba,cassos/mgba,libretro/mgba,askotx/mgba,sergiobenrocha2/mgba,fr500/mgba,Iniquitatis/mgba,zerofalcon/mgba,Anty-Lemon/mgba,AdmiralCurtiss/mgba,sergiobenrocha2/mgba,iracigt/mgba,jeremyherbert/mgba,fr500/mgba,fr500/mgba,cassos/mgba,MerryMage/mgba,libretro/mgba,cassos/mgba,iracigt/mgba,askotx/mgba,Iniquitatis/mgba,sergiobenrocha2/mgba,sergiobenrocha2/mgba,Anty-Lemon/mgba,iracigt/mgba,AdmiralCurtiss/mgba,Anty-Lemon/mgba,mgba-emu/mgba,mgba-emu/mgba,MerryMage/mgba,askotx/mgba,fr500/mgba,Touched/mgba,libretro/mgba,jeremyherbert/mgba,sergiobenrocha2/mgba,mgba-emu/mgba,askotx/mgba,iracigt/mgba,jeremyherbert/mgba,Iniquitatis/mgba,Touched/mgba,libretro/mgba,libretro/mgba,mgba-emu/mgba,Anty-Lemon/mgba,jeremyherbert/mgba